diff --git a/src/lib.rs b/src/lib.rs
index 7cb2af2..f770fa1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,102 +1,10 @@
-use crate::session_date_calculator::{Day, NthWeekday};
-use chrono::{NaiveDate, Weekday};
-use serde::{Deserialize, Serialize};
-use std::collections::HashMap;
+use crate::session_date_calculator::Day;
+use chrono::Weekday;
 
+pub mod session;
 pub mod session_date_calculator;
 pub mod webpage;
 
-#[derive(Debug, Clone)]
-pub struct DatedSession {
-  pub day: Day,
-  pub session: Session,
-  pub applying_exception: Option<Exception>,
-}
-
-impl Noted for DatedSession {
-  fn note(&self) -> Option<&String> {
-    match &self.applying_exception {
-      Some(e) => e.note(),
-      None => self.session.note(),
-    }
-  }
-}
-
-#[derive(Debug, Clone, Eq, PartialEq, Serialize, Deserialize)]
-pub enum Session {
-  Regular {
-    rule: NthWeekday,
-    note: Option<String>,
-    except: HashMap<NaiveDate, Exception>,
-  },
-  Extra {
-    date: NaiveDate,
-    note: Option<String>,
-  },
-}
-
-impl Session {
-  pub fn into_dated(self, day: Day) -> Result<DatedSession, Self> {
-    if !self.is_applicable_to(&day) {
-      return Err(self);
-    }
-
-    let dated_session = DatedSession {
-      applying_exception: match self {
-        Session::Regular { ref except, .. } => except.get(&day.date).cloned(),
-        _ => None,
-      },
-      session: self,
-      day,
-    };
-    Ok(dated_session)
-  }
-
-  pub fn is_applicable_to(&self, day: &Day) -> bool {
-    match *self {
-      Session::Regular { rule, .. } => rule.matches(day),
-      Session::Extra { date, .. } => day.date == date,
-    }
-  }
-}
-
-impl Noted for Session {
-  fn note(&self) -> Option<&String> {
-    match self {
-      Session::Regular { note, .. } => note,
-      Session::Extra { note, .. } => note,
-    }
-    .as_ref()
-  }
-}
-
-#[derive(Debug, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
-pub enum Exception {
-  Cancel {
-    note: Option<String>,
-  },
-  Alter {
-    #[serde(default)]
-    date: Option<NaiveDate>,
-    #[serde(default)]
-    note: Option<String>,
-  },
-}
-
-impl Noted for Exception {
-  fn note(&self) -> Option<&String> {
-    match self {
-      Exception::Cancel { note, .. } => note,
-      Exception::Alter { note, .. } => note,
-    }
-    .as_ref()
-  }
-}
-
-pub trait Noted {
-  fn note(&self) -> Option<&String>;
-}
-
 pub fn localize_day(day: &Day) -> String {
   format!(
     "{}, {}",
diff --git a/src/session.rs b/src/session.rs
new file mode 100644
index 0000000..1891913
--- /dev/null
+++ b/src/session.rs
@@ -0,0 +1,208 @@
+use crate::session_date_calculator::{Day, NthWeekday};
+use chrono::NaiveDate;
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+
+#[derive(Debug, Clone, Eq, PartialEq, Serialize, Deserialize)]
+pub struct DatedSession {
+  pub day: Day,
+  pub session: Session,
+  pub applying_exception: Option<Exception>,
+}
+
+impl Noted for DatedSession {
+  fn get_note(&self) -> Option<&String> {
+    match &self.applying_exception {
+      Some(e) => e.get_note(),
+      None => self.session.get_note(),
+    }
+  }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Serialize, Deserialize)]
+pub enum Session {
+  Regular(RegularSession),
+  Extra(ExtraSession),
+}
+
+impl From<RegularSession> for Session {
+  fn from(value: RegularSession) -> Self {
+    Self::Regular(value)
+  }
+}
+
+impl From<ExtraSession> for Session {
+  fn from(value: ExtraSession) -> Self {
+    Self::Extra(value)
+  }
+}
+
+impl Session {
+  pub fn into_dated(self, day: Day) -> Result<DatedSession, Self> {
+    if !self.is_applicable_to(&day) {
+      return Err(self);
+    }
+
+    let dated_session = DatedSession {
+      applying_exception: match self {
+        Session::Regular(RegularSession { ref except, .. }) => except.get(&day.date).cloned(),
+        _ => None,
+      },
+      session: self,
+      day,
+    };
+    Ok(dated_session)
+  }
+
+  pub fn is_applicable_to(&self, day: &Day) -> bool {
+    match *self {
+      Session::Regular(RegularSession { rule, .. }) => rule.matches(day),
+      Session::Extra(ExtraSession { date, .. }) => day.date == date,
+    }
+  }
+}
+
+impl Noted for Session {
+  fn get_note(&self) -> Option<&String> {
+    match self {
+      Session::Regular(session) => session.get_note(),
+      Session::Extra(session) => session.get_note(),
+    }
+  }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Serialize, Deserialize)]
+pub struct RegularSession {
+  pub rule: NthWeekday,
+  pub note: Option<String>,
+  pub except: HashMap<NaiveDate, Exception>,
+}
+
+impl From<NthWeekday> for RegularSession {
+  fn from(rule: NthWeekday) -> Self {
+    Self {
+      rule,
+      note: None,
+      except: Default::default(),
+    }
+  }
+}
+
+impl RegularSession {
+  pub fn with_exception<D, E>(mut self, date: D, exception: E) -> Self
+  where
+    D: Into<NaiveDate>,
+    E: Into<Exception>,
+  {
+    self.except.insert(date.into(), exception.into());
+    self
+  }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
+pub struct ExtraSession {
+  pub date: NaiveDate,
+  pub note: Option<String>,
+}
+
+impl From<NaiveDate> for ExtraSession {
+  fn from(date: NaiveDate) -> Self {
+    Self { date, note: None }
+  }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
+pub enum Exception {
+  Cancel(CancelException),
+  Alter(AlterException),
+}
+
+impl From<CancelException> for Exception {
+  fn from(value: CancelException) -> Self {
+    Self::Cancel(value)
+  }
+}
+
+impl From<AlterException> for Exception {
+  fn from(value: AlterException) -> Self {
+    Self::Alter(value)
+  }
+}
+
+impl Noted for Exception {
+  fn get_note(&self) -> Option<&String> {
+    match self {
+      Exception::Cancel(exception) => exception.get_note(),
+      Exception::Alter(exception) => exception.get_note(),
+    }
+  }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Default, Serialize, Deserialize)]
+#[serde(default)]
+pub struct CancelException {
+  pub note: Option<String>,
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Default, Serialize, Deserialize)]
+#[serde(default)]
+pub struct AlterException {
+  pub date: Option<NaiveDate>,
+  pub note: Option<String>,
+}
+
+impl From<NaiveDate> for AlterException {
+  fn from(value: NaiveDate) -> Self {
+    Self {
+      date: Some(value),
+      ..Self::default()
+    }
+  }
+}
+
+pub trait Noted {
+  fn get_note(&self) -> Option<&String>;
+}
+
+macro_rules! impl_noted {
+  ($ty: ident) => {
+    impl Noted for $ty {
+      fn get_note(&self) -> Option<&String> {
+        self.note.as_ref()
+      }
+    }
+  };
+}
+
+impl_noted!(RegularSession);
+impl_noted!(ExtraSession);
+impl_noted!(AlterException);
+impl_noted!(CancelException);
+
+pub trait WithNote {
+  fn with_note<S>(self, note: S) -> Self
+  where
+    S: ToString;
+}
+
+macro_rules! impl_with_node {
+  ($ty: ident) => {
+    impl WithNote for $ty {
+      fn with_note<S>(self, note: S) -> Self
+      where
+        S: ToString,
+      {
+        #[allow(clippy::needless_update)]
+        Self {
+          note: Some(note.to_string()),
+          ..self
+        }
+      }
+    }
+  };
+}
+
+impl_with_node!(AlterException);
+impl_with_node!(CancelException);
+impl_with_node!(ExtraSession);
+impl_with_node!(RegularSession);
diff --git a/src/session_date_calculator.rs b/src/session_date_calculator.rs
index 3d1e396..0ed3a5b 100644
--- a/src/session_date_calculator.rs
+++ b/src/session_date_calculator.rs
@@ -96,7 +96,7 @@ impl Iterator for DayIter {
   }
 }
 
-#[derive(Debug, Clone, Eq, PartialEq, Hash)]
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
 pub struct Day {
   pub date: NaiveDate,
   pub weekday: Weekday,